Vehicle exhaust gas recirculation system utilizing a low temperature circuit-high temperature circuit crossover valve assembly

ABSTRACT

The exhaust gas recirculation (EGR) system provided herein utilizes a crossover (X) valve that is selectively activated at the direction of the electronic control module (ECM) to mix the high temperature (HT) and low temperature (LT) circuits of the EGR system under certain predetermined operating conditions. Thus, HT circuit fluid (at engine temperatures) is selectively fed into the LT circuit fluid (at ambient temperatures) to heat certain LT circuit components that are normally cooled by the LT circuit before starting the low pressure (LP) EGR in certain cold cycles. When this heating is finished, the X valve is closed to provide normal HT circuit/LT circuit fluid separation. The X valve can be controlled using a rotational actuator or the like. To avoid exposing the LT circuit to the high revolution-per-minute (RPM) operating conditions of the HT circuit, a HT bypass mechanism is provided.

CROSS-REFERENCE TO RELATED APPLICATION

The present disclosure is a continuation of U.S. patent application Ser.No. 16/251,162, filed on Jan. 18, 2019, and entitled “VEHICLE EXHAUSTGAS RECIRCULATION SYSTEM UTILIZING A LOW TEMPERATURE CIRCUIT-HIGHTEMPERATURE CIRCUIT CROSSOVER VALVE ASSEMBLY,” the contents of which areincorporated in full by reference herein.

TECHNICAL FIELD

The present invention relates generally to the automotive field. Morespecifically, the present invention relates to a vehicle exhaust gasrecirculation (EGR) system utilizing a low temperature (LT) circuit-hightemperature (HT) circuit crossover (X) valve assembly to selectivelyavoid condensation in the exhaust gases recirculated to the associatedturbocharger compressor inlet, thereby avoiding subsequent compressorcomponent damage.

BACKGROUND

As fuel efficiency and emissions concerns become increasingly important,more and more vehicles are being equipped with turbochargers utilizingexhaust gas recirculation (EGR) systems. EGR systems increase the fuelefficiency of an internal combustion (IC) engine and reduce theemissions of noxious exhaust gases by recirculating a portion of theunused fuel and exhaust gases back to the engine for subsequent use,instead of releasing them into the environment. In a low pressure (LP)EGR system, the exhaust gases are reintroduced to the engine justupstream of the turbocharger compressor, at the turbocharger compressorinlet. At this location, the pressure is low, even under high engineboost conditions. This solves some of the quality issues associated withrelated high pressure (HP) EGR systems.

As illustrated in FIG. 1, EGR gases are mixed with conventional inletair just before entering the turbocharger compressor. The ratio of EGRgases to inlet air determines the efficiency of the EGR system andengine overall. The utilization of EGR gases, however, is often limitedby the condensation of water droplets in the EGR gases near the mixingpoint as the hot, humid EGR gases are cooled by the cool, dry inlet air.This cooling usually occurs through (and condensation usually occurs onand adjacent to) the wall that divides the hot, humid EGR gases from thecool, dry inlet air just prior to the mixing point, in the hot, humidEGR gases. This problem is especially pronounced under cold start andlow temperature operating conditions, sometimes delaying the normalactivation of the EGR system. This can compromise emissions testingresults, for example, and otherwise degrade engine performance. In aworst case scenario, under extreme conditions, ice particles can even beformed in the EGR gases, exacerbating these issues.

Problematically, the condensed water droplets (or ice particles) nearthe mixing point of the EGR gases and the inlet air are fed directly tothe turbocharger compressor. These water droplets (or ice particles) canimpact the turbocharger compressor wheel, blades, and other components,damaging them. As illustrated in FIG. 2, the water droplets initiallyexert a force perpendicular to the component surface, which causes ablast wave upon component surface contact, resulting in a force exertedparallel to the component surface. This force exerted parallel to thecomponent surface can impinge upon surface imperfections, causingspalls, cracks, etc. at or near such surface imperfections.

Thus, what is still needed in the art is an EGR system that inhibits thecondensation of water droplets and the formation of ice particles nearthe mixing point of the associated EGR gases and inlet air, andespecially on and adjacent to the wall separating the EGR gases from theinlet air, such that the subsequent turbocharger compressor wheel,blades, and other components are not damaged by the condensed waterdroplets or formed ice particles. One way this can be done is throughthe selective high temperature (HT) circuit heating of low temperature(LT) circuit components (e.g., the water-cooled charge air cooler(WCAC), compressor, selective catalytic reducer (SCR), etc.) that arenormally cooled by the LT circuit before starting the LP EGR in certaincold cycles. This circuit shifting can be controlled by an electroniccontrol module (ECM) to target a setpoint temperature that avoidscondensation risks at subzero conditions, for example.

SUMMARY

Accordingly, the exhaust gas recirculation (EGR) system provided hereinutilizes a crossover (X) valve that is selectively activated at thedirection of the electronic control module (ECM) to mix the hightemperature (HT) and low temperature (LT) circuits of the EGR systemunder certain predetermined operating conditions. Thus, HT circuit fluid(at engine temperatures) is selectively fed into the LT circuit fluid(at ambient temperatures) to heat certain LT circuit components (e.g.,the water-cooled charge air cooler (WCAC), compressor, selectivecatalytic reducer (SCR), etc.) that are normally cooled by the LTcircuit before starting the low pressure (LP) EGR in certain coldcycles. When this heating is finished, the X valve is closed to providenormal HT circuit/LT circuit fluid separation. In operation, the fixeddisplacement HT pump flow curve follows engine revolutions-per-minute(RPM), while the electrical LT pump flow curve follows a softwarealgorithm incorporating a temperature model. The X valve can becontrolled using a rotational actuator or the like that is coupled tothe X valve and ultimately actuated by the ECM. To avoid exposing the LTcircuit to the high RPM operating conditions of the HT circuit, inaddition to electrical LT pump flow curve control, a HT bypass mechanismis provided.

The X valve provided herein effectively inhibits the condensation ofwater droplets and the formation of ice particles near and at the mixingpoint of the EGR gases and inlet air in the upstream proximity of thecompressor inlet, such that the turbocharger compressor wheel, blades,and other components are not subsequently damaged by the condensed waterdroplets or formed ice particles. This inhibition can be targeted tocertain known problematic operating conditions.

In one exemplary embodiment, the vehicle exhaust gas recirculation (EGR)system provided herein includes: a high temperature (HT) circuit adaptedto circulate a relatively higher temperature fluid within the EGRsystem; a low temperature (LT) circuit adapted to circulate a relativelylower temperature fluid within the EGR system; and means for selectivelymixing all or a portion of the relatively higher temperature fluid ofthe HT circuit with the relatively lower temperature fluid of the LTcircuit fluidly coupled to both the HT circuit and the LT circuit.

In another exemplary embodiment, the crossover (X) valve assembly forthe vehicle exhaust gas recirculation (EGR) system provided hereinincludes: a valve housing; a low temperature (LT) inlet port fluidlycoupled to the housing; a LT outlet port fluidly coupled to the housing,the LT inlet port and the LT outlet port forming a portion of a LTcircuit adapted to circulate a relatively lower temperature fluid withinthe EGR system; a high temperature (HT) inlet port fluidly coupled tothe housing; a HT outlet port fluidly coupled to the housing, the HTinlet port and the HT outlet port forming a portion of a HT circuitadapted to circulate a relatively higher temperature fluid within theEGR system; and an inner wall disposed within the valve housing adaptedto be actuated from an inactive configuration in which the LT inlet portis fluidly coupled to the LT outlet port through a LT chamber definedwithin the valve housing and the HT inlet port is fluidly coupled to theHT outlet port through a HT chamber defined within the valve housing andan active configuration in which the HT inlet port is fluidly coupled tothe LT outlet port through a first mixing chamber defined within thevalve housing and the LT inlet port is fluidly coupled to the HT outletport through a second mixing chamber defined within the valve housing.

In a further exemplary embodiment, the computer program product providedherein includes a non-transitory computer readable medium havinginstructions stored thereon and executed to cause a computer to: obtainan operating state of a vehicle; and, based on the obtained operatingstate of the vehicle, selectively actuate a valve assembly fluidlycoupled to a high temperature (HT) circuit adapted to circulate arelatively higher temperature fluid within an exhaust gas recirculation(EGR) system and a low temperature (LT) circuit adapted to circulate arelatively lower temperature fluid within the EGR system, actuating thevalve assembly causing all or a portion of the relatively highertemperature fluid of the HT circuit to mix with the relatively lowertemperature fluid of the LT circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated and described herein with referenceto the various drawings, in which like reference numbers are used todenote like system or assembly components/method or algorithm steps, asappropriate, and in which:

FIG. 1 is a cut-away perspective view of a conventional ported shroudand compressor inlet area of an EGR system, highlighting the problematiccondensation of water droplets near the mixing point of the associatedEGR gases and inlet air;

FIG. 2 is a schematic diagram illustrating the mechanism by whichcondensed water droplets can damage a turbocharger compressor component;

FIG. 3 is a schematic diagram illustrating one exemplary embodiment ofthe EGR system provided herein, allowing for selective crossover of theHT and LT circuits for the selective heating of LT circuit components;

FIG. 4 is a perspective view of one exemplary embodiment of the X valveprovided herein and used in the EGR system of FIG. 3;

FIG. 5 is a series of schematic diagrams illustrating one exemplaryoperation method of the X valve of FIG. 4, incorporating an external HTcircuit bypass;

FIG. 6 is a series of schematic diagrams illustrating another exemplaryoperation method of the X valve of FIG. 4, incorporating an internal HTcircuit bypass;

FIG. 7 is a series of schematic diagrams illustrating a furtherexemplary operation method of the X valve of FIG. 4, incorporating anexternal HT circuit bypass utilizing a check valve;

FIG. 8 is a series of schematic diagrams illustrating a still furtherexemplary operation method of the X valve of FIG. 4, incorporating aninternal HT circuit bypass utilizing a check valve; and

FIG. 9 is a series of schematic diagrams illustrating a still furtherexemplary operation method of the X valve of FIG. 4, highlighting theuse of different valve body configurations to regulate the flowtransition between the HT and LT circuits.

DESCRIPTION OF EMBODIMENTS

Again, the exhaust gas recirculation (EGR) system provided hereinutilizes a crossover (X) valve that is selectively activated at thedirection of the electronic control module (ECM) to mix the hightemperature (HT) and low temperature (LT) circuits of the EGR systemunder certain predetermined operating conditions. Thus, HT circuit fluid(at engine temperatures) is selectively fed into the LT circuit fluid(at ambient temperatures) to heat certain LT circuit components (e.g.,the water-cooled charge air cooler (WCAC), compressor, selectivecatalytic reducer (SCR), etc.) that are normally cooled by the LTcircuit before starting the low pressure (LP) EGR in certain coldcycles. When this heating is finished, the X valve is closed to providenormal HT circuit/LT circuit fluid separation. In operation, the fixeddisplacement HT pump flow curve follows engine revolutions-per-minute(RPM), while the electrical LT pump flow curve follows a softwarealgorithm incorporating a temperature model. The X valve can becontrolled using a rotational actuator or the like that is coupled tothe X valve and ultimately actuated by the ECM. To avoid exposing the LTcircuit to the high RPM operating conditions of the HT circuit, inaddition to electrical LT pump flow curve control, a HT bypass mechanismis provided.

The X valve provided herein effectively inhibits the condensation ofwater droplets and the formation of ice particles near and at the mixingpoint of the EGR gases and inlet air in the upstream proximity of thecompressor inlet, such that the turbocharger compressor wheel, blades,and other components are not subsequently damaged by the condensed waterdroplets or formed ice particles. This inhibition can be targeted tocertain known problematic operating conditions.

Referring now specifically to FIG. 3, in one exemplary embodiment, theEGR system 100 provided herein includes a HT circuit 102 that circulatesa fluid at roughly engine temperatures and a LT circuit 104 thatcirculates a fluid at roughly ambient temperatures. The HT circuit 102includes a fixed displacement pump 106 that utilizes a flow curve thatis defined by engine operating RPM. The LT circuit 104 includes anelectrical pump 108 that is software controlled, using a temperaturemodel that, in part, dictates the operation described herein. Othercomponents of the HT circuit 102 and the LT circuit 104, and the EGRsystem 100 in general, are well known to those of ordinary skill in theart and are not described in greater detail herein. The EGR system 100incorporates a X valve 110 that selectively intermingles the HT circuit102 with the LT circuit 104, with HT fluid being added to the LT fluidto selectively heat various components (e.g., the water-cooled chargeair cooler (WCAC), compressor, selective catalytic reducer (SCR), etc.)of the LT circuit 104. When this heating process is finished and nolonger needed, the X valve 110 effectively separates the HT circuit 102and the LT circuit 104, as normal. As alluded to herein above, to avoidexposing the LT circuit 104 to the high RPM operating conditions of theHT circuit 102, in addition to electrical LT pump flow curve control, aHT bypass mechanism is optionally provided.

Referring now specifically to FIG. 4, the X-valve 110 provided herein isa 4-port rotational valve assembly or the like, including a LT inletport 112, a LT outlet port 114, a HT inlet port 116, and a HT outletport 118. In an inactive configuration, the X-valve separates the LTports 112, 114 from the HT ports 116, 118, while providing through pathsfor the appropriate LT circuit 102 (FIG. 3) or HT circuit 104 (FIG. 3).In an active configuration, the X-valve 110 allows some of the higherpressure HT fluid to infiltrate the LT fluid. The X valve 110 iscontrolled using a rotational actuator 120 or the like that is coupledto the X valve 110 and ultimately actuated by the ECM (not illustrated).In general, the 4-port rotational valve assembly or the like isconventional in that it includes a housing and an internal flowdiverting structure, as is described in greater detail herein below. Toavoid exposing the LT circuit 104 to the high RPM operating conditionsof the HT circuit 102, in addition to electrical LT pump flow curvecontrol, a HT bypass mechanism, also described in greater detail hereinbelow, is optionally provided. Not only does this HT bypass mechanismsafeguard the LT circuit 104, it also limits the increased load on theHT pump 106 (FIG. 3).

Referring now specifically to FIG. 5, in one exemplary embodiment, in aninactive configuration, the X valve 110 separates the LT circuit 104(FIG. 3) from the HT circuit 102 (FIG. 3) by providing a LT flow chamber124 within the valve housing 121. The LT flow chamber 124 couples the LTinlet port 112 and the LT outlet port 114. The X valve 110 provides a HTflow chamber 126 within the valve housing 121 that couples the HT inletport 116 and the HT outlet port 118. The LT flow chamber 124 isseparated from the HT flow chamber 126 by an inner wall 122 orcomparable mechanism. In this exemplary embodiment, the inner wall 122is rotationally deployed. An external HT bypass 128 is provided thatshunts a portion of the HT fluid around the X valve 110 at all times,thereby maintaining a HT fluid flow and limiting over-pressurization ofthe LT circuit 104. In an active configuration, in this exemplaryembodiment, the inner wall 122 is rotated approximately 90 degrees toform a first mixing chamber 130 within the valve housing 121 thatprovides some of the HT fluid from the HT inlet port 116 to the LToutlet port 114, thereby heating the LT circuit 104. The inner wall 122also forms a second mixing chamber 132 within the valve housing 121 thatprovides all of the LT fluid from the LT inlet port 112 to the HT outletport 118, thereby cooling the HT circuit 102. Again, the external HTbypass 128 is provided that shunts a portion of the HT fluid around theX valve 110 at all times, thereby maintaining a HT fluid flow andlimiting over-pressurization of the LT circuit 104.

Referring now specifically to FIG. 6, in another exemplary embodiment,in an inactive configuration, the X valve 110 separates the LT circuit104 (FIG. 3) from the HT circuit 102 (FIG. 3) by providing a LT flowchamber 124 within the valve housing 121. The LT flow chamber 124couples the LT inlet port 112 and the LT outlet port 114. The X valve110 provides a HT flow chamber 126 within the valve housing 121 thatcouples the HT inlet port 116 and the HT outlet port 118. The LT flowchamber 124 is separated from the HT flow chamber 126 by an inner wall122 or comparable mechanism. In this exemplary embodiment, the innerwall 122 is rotationally deployed. An internal HT bypass 134 is providedthat shunts a portion of the HT fluid around the LT circuit 104 withinthe valve housing 121 when the X-valve 110 is actuated, therebymaintaining a HT fluid flow and limiting over-pressurization of the LTcircuit 104. In an active configuration, in this exemplary embodiment,the inner wall 122 is rotated approximately 90 degrees to form a firstmixing chamber 130 within the valve housing 121 that provides some ofthe HT fluid from the HT inlet port 116 to the LT outlet port 114,thereby heating the LT circuit 104. The inner wall 122 also forms asecond mixing chamber 132 within the valve housing 121 that provides allof the LT fluid from the LT inlet port 112 to the HT outlet port 118,thereby cooling the HT circuit 102. Again, the internal HT bypass 134 isprovided that shunts a portion of the HT fluid around the LT circuit 104within the valve housing 121 when the X-valve 110 is actuated, therebymaintaining a HT fluid flow and limiting over-pressurization of the LTcircuit 104. In this exemplary embodiment, the internal HT bypass 134 isformed via a 2-piece inner wall 122. The inner wall 122 is intact in theinactive configuration, but is split into two pieces in the activeconfiguration, with one piece of the inner wall 122 rotating asdescribed, and another piece of the inner wall 122 remaining in itsoriginal position. This effectively forms the internal HT bypass 134, astwo HT paths are provided, one to the LT outlet port 114 through thefirst mixing chamber 130 and one to the HT outlet port 118 through theinner wall 122.

Referring now specifically to FIG. 7, in a further exemplary embodiment,in an inactive configuration, the X valve 110 separates the LT circuit104 (FIG. 3) from the HT circuit 102 (FIG. 3) by providing a LT flowchamber 124 within the valve housing 121. The LT flow chamber 124couples the LT inlet port 112 and the LT outlet port 114. The X valve110 provides a HT flow chamber 126 within the valve housing 121 thatcouples the HT inlet port 116 and the HT outlet port 118. The LT flowchamber 124 is separated from the HT flow chamber 126 by an inner wall122 or comparable mechanism. In this exemplary embodiment, the innerwall 122 is rotationally deployed. An external HT bypass 128 is providedthat shunts a portion of the HT fluid around the X valve 110, therebymaintaining a HT fluid flow and limiting over-pressurization of the LTcircuit 104. The external HT bypass 128 incorporates a check valve 136or the like, described in greater detail herein below. In an activeconfiguration, in this exemplary embodiment, the inner wall 122 isrotated approximately 90 degrees to form a first mixing chamber 130within the valve housing 121 that provides some of the HT fluid from theHT inlet port 116 to the LT outlet port 114, thereby heating the LTcircuit 104. The inner wall 122 also forms a second mixing chamber 132within the valve housing 121 that provides all of the LT fluid from theLT inlet port 112 to the HT outlet port 118, thereby cooling the HTcircuit 102. Again, the external HT bypass 128 is provided that shunts aportion of the HT fluid around the X valve 110, thereby maintaining a HTfluid flow and limiting over-pressurization of the LT circuit 104. Theexternal HT bypass 128 incorporates a check valve 136 or the like. Thischeck valve 136 ensures that the HT circuit 102 feeds LT circuit 104 atlow mass flows, when 100% of the heated mass flow is diverted to heatthe LT circuit 104. The check valve 136 open to manage high mass flows,when the pressure exceeds the check valve pressure, thus avoidingcavitation and HT pump issues.

Referring now specifically to FIG. 8, in a still further exemplaryembodiment, in an inactive configuration, the X valve 110 separates theLT circuit 104 (FIG. 3) from the HT circuit 102 (FIG. 3) by providing aLT flow chamber 124 within the valve housing 121. The LT flow chamber124 couples the LT inlet port 112 and the LT outlet port 114. The Xvalve 110 provides a HT flow chamber 126 within the valve housing 121that couples the HT inlet port 116 and the HT outlet port 118. The LTflow chamber 124 is separated from the HT flow chamber 126 by an innerwall 122 or comparable mechanism. In this exemplary embodiment, theinner wall 122 is rotationally deployed. An internal HT bypass 138 isbuilt into the inner wall 122 that shunts a portion of the HT fluidaround the LT circuit 104, thereby maintaining a HT fluid flow andlimiting over-pressurization of the LT circuit 104. The internal HTbypass 138 incorporates a check valve 140 or the like, described ingreater detail herein below. In an active configuration, in thisexemplary embodiment, the inner wall 122 is rotated approximately 90degrees to form a first mixing chamber 130 within the valve housing 121that provides some of the HT fluid from the HT inlet port 116 to the LToutlet port 114, thereby heating the LT circuit 104. The inner wall 122also forms a second mixing chamber 132 within the valve housing 121 thatprovides all of the LT fluid from the LT inlet port 112 to the HT outletport 118, thereby cooling the HT circuit 102. Again, the internal HTbypass 138 is is built into the inner wall 122 that shunts a portion ofthe HT fluid around the LT circuit 104, thereby maintaining a HT fluidflow and limiting over-pressurization of the LT circuit 104. Theinternal HT bypass 138 incorporates a check valve 140 or the like. Thischeck valve 140 ensures that the HT circuit 102 feeds LT circuit 104 atlow mass flows, when 100% of the heated mass flow is diverted to heatthe LT circuit 104. The check valve 140 open to manage high mass flows,when the pressure exceeds the check valve pressure, thus avoidingcavitation and HT pump issues.

As illustrated in FIG. 9, the shape of the interior of the valve housing121 and inner wall 122 can be varied to tailor the flows associated withthe HT circuit 102 (FIG. 3) and the LT circuit 104 (FIG. 3) within the Xvalve 110. For example, the inner wall 122 can have one or morethickened and/or angled portions, the inner wall 122 can have one ormore concave/convex surfaces, and/or the interior of the valve housing121 and/or inner wall 122 can define one or more discrete fluid flowchannels. All of these features help to define fluid flow volume andvelocity, as well as degree of HT/LT mixing, avoiding turbulence.

The software algorithm contemplated herein determines the desiredoperating state of the associated vehicle and adjusts the HT/LT mix asappropriate, in accordance with the description herein. Preferably, thesoftware algorithm is implemented as coded instructions stored in amemory and executed by a processor. The processor is a hardware devicefor executing such coded instructions. The processor can be any custommade or commercially available processor, a central processing unit(CPU), an auxiliary processor among several processors associated withthe memory, a semiconductor-based microprocessor (in the form of amicrochip or chip set), or generally any device for executing codedinstructions. The processor is configured to execute software storedwithin the memory to communicate data to and from the memory, and togenerally control operations pursuant to the coded instructions. In anexemplary embodiment, the processor may include a mobile optimizedprocessor, such as one optimized for power consumption and mobileapplications. I/O interfaces can be used to receive user input and/orfor providing system output. User input can be provided via, forexample, a keypad, a touch screen, a scroll ball, a scroll bar, buttons,and/or the like. System output can be provided via a display device,such as a liquid crystal display (LCD), touch screen, and/or the like.The I/O interfaces can also include, for example, a serial port, aparallel port, a small computer system interface (SCSI), an infrared(IR) interface, a radio frequency (RF) interface, a universal serial bus(USB) interface, and/or the like. The I/O interfaces can include a GUIthat enables a user to interact with the memory. Additionally, the I/Ointerfaces may further include an imaging device, i.e. camera, videocamera, sensors, etc., as described herein.

The memory may include any of volatile memory elements (e.g., randomaccess memory (RAM, such as DRAM, SRAM, SDRAM, etc.)), nonvolatilememory elements (e.g., ROM, hard drive, etc.), and combinations thereof.Moreover, the memory may incorporate electronic, magnetic, optical,and/or other types of storage media. Note that the memory may have adistributed architecture, where various components are situated remotelyfrom one another, but can be accessed by the processor. The software inmemory can include one or more software programs, each of which includesan ordered listing of executable instructions for implementing logicalfunctions. The software in the memory includes a suitable operatingsystem (O/S) and programs. The operating system essentially controls theexecution of other computer programs, and provides scheduling,input-output control, file and data management, memory management, andcommunication control and related services. The programs may includevarious applications, add-ons, etc. configured to provide end userfunctionality. The programs can include an application or “app” whichprovides various functionalities.

Again, the X valve and methodologies provided herein effectivelyinhibits the condensation of water droplets and the formation of iceparticles near and at the mixing point of the EGR gases and inlet air inthe upstream proximity of the compressor inlet, such that theturbocharger compressor wheel, blades, and other components are notsubsequently damaged by the condensed water droplets or formed iceparticles. This inhibition can be targeted to certain known problematicoperating conditions.

Although the present invention is illustrated and described herein withreference to preferred embodiments and specific examples thereof, itwill be readily apparent to those of ordinary skill in the art thatother embodiments and examples can perform similar functions and/orachieve like results. All such equivalent embodiments and examples arewithin the spirit and scope of the present invention, are contemplatedthereby, and are intended to be covered by the following non-limitingclaims for all purposes.

What is claimed is:
 1. An exhaust gas recirculation (EGR) system for avehicle, the EGR system comprising: a high temperature (HT) circuitadapted to circulate a relatively higher temperature fluid within theEGR system; a low temperature (LT) circuit adapted to circulate arelatively lower temperature fluid within the EGR system; and acrossover (X) valve assembly adapted to selectively mix all or a portionof the relatively higher temperature fluid of the HT circuit with therelatively lower temperature fluid of the LT circuit fluidly coupled toboth the HT circuit and the LT circuit, wherein the X valve assemblycomprises a valve housing encompassing an inner wall adapted to define,in an active configuration, a first mixing chamber fluidly coupling a HTinlet port to a LT outlet port of the valve housing and a second mixingchamber fluidly coupling a LT inlet port to a HT outlet port of thevalve housing, and wherein the X valve assembly comprises a HT bypassmechanism adapted to bypass a portion of the relatively highertemperature fluid of the HT circuit around or through the X valveassembly from the HT inlet port to the HT outlet port of the valvehousing.
 2. The EGR system of claim 1, wherein the HT circuit comprisesa fixed displacement HT pump adapted to operate with a flow curve thatfollows engine revolutions-per-minute (RPM).
 3. The EGR system of claim1, wherein the LT circuit comprises an electrical LT pump adapted tooperate with a flow curve that follows a vehicle operating temperaturemodel.
 4. The EGR system of claim 1, wherein the X valve assembly isadapted to be rotationally actuated by an electronic control module(ECM) of the vehicle.
 5. The EGR system of claim 1, wherein the HTbypass mechanism comprises a check valve adapted to bypass the portionof the relatively higher temperature fluid of the HT circuit around orthrough the X valve assembly based on a mass flow rate of the relativelyhigher temperature fluid.
 6. The EGR system of claim 1, wherein theinner wall of the X valve assembly has a variable thickness.
 7. The EGRsystem of claim 1, wherein the inner wall of the X valve assemblycomprises one or more of an angled surface, a concave surface, and aconvex surface.
 8. A crossover (X) valve assembly for a vehicle exhaustgas recirculation (EGR) system, the X valve assembly comprising: a valvehousing; a low temperature (LT) inlet port fluidly coupled to thehousing; a LT outlet port fluidly coupled to the housing, the LT inletport and the LT outlet port forming a portion of a LT circuit adapted tocirculate a relatively lower temperature fluid within the EGR system; ahigh temperature (HT) inlet port fluidly coupled to the housing; a HToutlet port fluidly coupled to the housing, the HT inlet port and the HToutlet port forming a portion of a HT circuit adapted to circulate arelatively higher temperature fluid within the EGR system; an inner walldisposed within the valve housing adapted to be actuated to an activeconfiguration in which the HT inlet port is fluidly coupled to the LToutlet port through a first mixing chamber defined within the valvehousing and the LT inlet port is fluidly coupled to the HT outlet portthrough a second mixing chamber defined within the valve housing; and aHT bypass mechanism disposed adjacent to the valve housing or throughthe inner wall and adapted to bypass a portion of the relatively highertemperature fluid of the HT circuit around or through the valve housingfrom the HT inlet port to the HT outlet port.
 9. The X valve assembly ofclaim 8, wherein the inner wall is adapted to be rotationally actuatedby an electronic control module (ECM) of a vehicle.
 10. The X valveassembly of claim 8, wherein the HT bypass mechanism disposed adjacentto the valve housing or through the inner wall comprises a check valveadapted to bypass the portion of the relatively higher temperature fluidof the HT circuit around or through the valve housing based on a massflow rate of the relatively higher temperature fluid.
 11. The X valveassembly of claim 8, wherein the inner wall has a variable thickness.12. The X valve assembly of claim 8, wherein the inner wall comprisesone or more of an angled surface, a concave surface, and a convexsurface.
 13. A computer program product including a non-transitorycomputer readable medium having instructions stored thereon and executedto cause a computer to: obtain an operating state of a vehicle; andbased on the obtained operating state of the vehicle, selectivelyactuate a valve assembly fluidly coupled to a high temperature (HT)circuit adapted to circulate a relatively higher temperature fluidwithin an exhaust gas recirculation (EGR) system and a low temperature(LT) circuit adapted to circulate a relatively lower temperature fluidwithin the EGR system, actuating the valve assembly causing all or aportion of the relatively higher temperature fluid of the HT circuit tomix with the relatively lower temperature fluid of the LT circuit;wherein the valve assembly comprises a crossover (X) valve assemblyfluidly coupled to both the HT circuit and the LT circuit, wherein the Xvalve assembly comprises a valve housing encompassing an inner walladapted to define, in an active configuration, a first mixing chamberfluidly coupling a HT inlet port to a LT outlet port of the valvehousing and a second mixing chamber fluidly coupling a LT inlet port toa HT outlet port of the valve housing, and wherein the X valve assemblycomprises a HT bypass mechanism adapted to bypass a portion of therelatively higher temperature fluid of the HT circuit around or throughthe X valve assembly from the HT inlet port to the HT outlet port of thevalve housing.
 14. The computer program product of claim 13, wherein theinstructions are further executed to cause the computer to, based on theobtained operating state of the vehicle, modify a flow of the relativelylower temperature fluid using an electrical LT pump that is fluidlycoupled to the LT circuit.
 15. The computer program product of claim 13,wherein the X valve assembly is adapted to be rotationally actuated. 16.The computer program product of claim 13, wherein the HT bypassmechanism comprises a check valve adapted to bypass the portion of therelatively higher temperature fluid of the HT circuit around or throughthe X valve assembly based on a mass flow rate of the relatively highertemperature fluid.
 17. The computer program product of claim 13, whereinthe instructions are further executed to cause the computer to: obtain asubsequent operating state of the vehicle; and based on the obtainedsubsequent operating state of the vehicle, selectively subsequentlyactuate the valve assembly fluidly coupled to the HT circuit adapted tocirculate the relatively higher temperature fluid within the EGR systemand the LT circuit adapted to circulate the relatively lower temperaturefluid within the EGR system, subsequently actuating the valve assemblycausing the relatively higher temperature fluid of the HT circuit to beseparated from the relatively lower temperature fluid of the LT circuit.18. The computer program product of claim 13, wherein the inner wall ofthe X valve assembly has a variable thickness.
 19. The computer programproduct of claim 13, wherein the inner wall of the X valve assemblycomprises one or more of an angled surface, a concave surface, and aconvex surface.